@Murugesan, Uthaya Kumar, Thanks for posting in Q&A.
From your description, I know you were in troubleshoot while enroll your new iPhone into Intune.
To clarify this issue, please check the following.
1.Please check whether this device displays in the Intune portal and Azure AD portal.
2.Please check whether deploying the conditional access policy. If yes, could you please provide the screen shots of the conditional access policy?
3.Please check the sign-in log in Microsoft Entra portal. Microsoft Entra portal > Protection > Conditional Access > Sign-in logs.
If there is any update, feel free to let me know.
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